The use of fluorescent liquid inks is well-known for the application of information to various types of documents which are intended to be exposed to ultraviolet radiation and then processed or read by means of detection machines. Such inks are widely used for the application of data information to checks for the indication of amounts, dates, banks involved, etc., enabling the checks to be sorted and routed automatically by processing machines.
The conventional fluorescent inks are liquid inks which are applied to the intended documents by means of fabric printing ribbons or ink pads. In many cases, different images and data are applied to the same document using different inks to provide information which is automatically sensible by optical, magnetic or other sensing devices. In such cases the fluorescing images frequently are applied over said other images such as over black optical or magnetic images.
Different fluorescing dyes have different colors and emit different wave-length radiation when exposed to and excited by ultraviolet radiation. The processing machines are quite sensitive and can be adjusted to detect and recognize either strong or weak signals within the emitted wavelength range. This adjustment requirement is necessitated by the fact that some detectible images are relatively poor in mass and/or quality or are absorbed and broadened when applied as liquid inks to porous copy papers so as to provide relatively weak signals while other detectible images are of good mass and quality and emit strong signals. The processing machine can be adjusted to read strong or weak signals but cannot reliably read both strong and weak signals emitted by images present on the same document. If the images cannot be read by the processing machine, the document is rejected and must be processed manually. In some cases, the imperfect images will be misread by the processing machine, causing errors. These defects frustrate the entire purpose of the system.
One of the most common causes of defective results in the system arises from the fact that the fluorescent inks frequently are typed or printed in overlapping relation over pre-applied images of contrasting color, i.e., over black images or bar codes comprising magnetic or optical inks. The fluorescing images, or portions thereof, applied directly to the light-colored paper stock emit strong signals under irradiation while the fluorescing images, or portions thereof, applied over the black images or bar codes, provide substantially weaker signals under irradiation. The sensitivity of the processing machine can be adjusted for the accurate recognition of the weak signals but such adjustment results in a loss of reliability with respect to the sensing of the strong signals, and vice-versa.